Medical images are commonly stored using the DICOM standard. Metadata in the form of DICOM data elements can be used to categorize and semantically describe the medical images. The DICOM data elements or other metadata can be used to provide information such as the gender of a patient, a modality used to obtain a medical image, the anatomical area or feature scanned to obtain the medical image, and a range of other information relating, for example, to the patient, the scanner used to obtain medical image data, parameters of the scan itself, and date and time information.
The DICOM standard defines a range of attributes, which may be used to describe the properties of an information object. Each DICOM attribute is described by a pair of numbers (group number, data element number) which may be referred to as a tag. A list of certain DICOM attributes and tags is provided for example in the document Digital Imaging and Communications in Medicine (DICOM), Part 6: Data Dictionary, published by National Electrical Manufacturers Association, 1300 N.17th Street, Rosslyn, Va. 22209, USA.
The values of DICOM attributes for a particular information object may be encoded as DICOM data elements. Each data element may comprise the relevant tag and a value. In some circumstances, the DICOM attributes or data elements themselves may be referred to as tags.
Although a large number of attributes are available under the DICOM standard, it is often the case that many of the corresponding data elements for particular medical images are not populated with data. Furthermore, it has been found that data included in DICOM data elements that are populated for particular medical images is incorrect. That is often the case for anatomical data, for example data identifying particular anatomical features or regions that are the subject of a scan.
It is also the case for at least some known systems that for many of the attributes, particularly attributes relating to anatomical features such as Body Part Examined (0008, 0015) or Anatomic Structure (0008, 2208), a user may have a free choice of text or other data with which to populate data elements, rather than being constrained to a choice of standard terms. For example, although it is recommended in at least some systems to use an anatomical region code defined by the SNOMED lexicon to populate Anatomic Structure (0008, 2208) in the DICOM standard, that is not mandatory. Thus, even if an anatomical feature or region is identified correctly in one or more DICOM data elements for a particular set of medical image data, the same anatomical feature or region may be identified in data elements for another set of medical image data using different terms. Furthermore, typographical or other errors may occur when entering text or other data.
In addition, there can in practice be ambiguity or overlap between possible terms relating to anatomical features for use in populating data elements, or confusion on the part of an operator as to which terms should be used, particularly if a scan covers several body parts or regions, or overlaps more than one region (for example head and neck).
In some systems, certain DICOM data elements relating to anatomical features (for example Body Part Examined) may be set automatically based on a selection of imaging parameters by an operator, for example based on selection of an examination protocol. For instance, in some systems if an operator selects an examination protocol of a scanner suitable for scanning, say, a patient's head, imaging parameters are set by the scanner based on that selection, and a DICOM data element or data elements are automatically populated to indicate that the scan is of a head. However, in practice operators may select an examination protocol for one anatomical region (for example Head) even though the scan is of another anatomical region (for example, Abdomen) if they are aware that the scan parameters for the selected examination protocol are likely to produce a good image quality. Thus, DICOM data elements can be automatically populated with incorrect anatomical information in some cases.
There are significant potential issues if DICOM data elements are incorrectly assigned to sets of image data, particularly given the very large quantities of image data that are now stored in Picture Archiving and Communication Systems (PACS) and other large scale medical data storage systems. For example, patient image data may be incorrectly categorized, or patient image data may be lost or ignored. In some cases, incorrect DICOM data or other metadata may potentially lead to errors in diagnosis.